In a tonal language, the identity of a word depends largely on the tonal identification of the contour of vocal fundamental frequency energy of which usually centers in a low frequency of less than 600 Hz. However, cochlear dead region (DR) is present mostly in the frequency range of 2000 Hz to 4000 Hz, and the effect of DR on a tonal language is worth investigating. Thirty-two native Mandarin speakers with moderate-to-severe degree of sensorineural hearing loss were included in this study. The pure-tone audiometry, speech recognition threshold (SRT) and word recognition score (WRS) were used to evaluate the degree of hearing loss and word recognition. The threshold equalizing noise (TEN) tests were used to identify the presence of DR. The results showed that most DRs were present in high frequencies. The hearing thresholds of the ears with a DR were not significantly different from those without DR. However, the WRS was significantly worse for the DR ears, especially for those whose DR included three or more audiometric frequencies. A DR caused a significantly worse word recognition for the tonal language speakers of Mandarin in Taiwan, although the DR frequency occurred in the high frequency of 2000 Hz to 4000 Hz.